1. Field of the Invention
Embodiments of the present invention generally relate to adaptive loop filtering for video coding.
2. Description of the Related Art
The Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T WP3/16 and ISO/IEC JTC 1/SC 29/WG 11 is currently developing the next-generation video coding standard referred to as High Efficiency Video Coding (HEVC). HEVC is expected to provide around 50% reduction in bit rate (at similar visual quality) over the current standard, H.264/AVC, and intended to support larger resolutions and higher frame rates. To address these requirements, HEVC utilizes larger block sizes than H.264/AVC. In HEVC, the largest coding unit (LCU) can be up to 64×64 in size, while in H.264/AVC, the macroblock size is fixed at 16×16.
In a coding scheme that uses block-based prediction, transform coding, and quantization, some characteristics of the compressed video data may differ from the original video data. For example, discontinuities referred to as blocking artifacts can occur in the reconstructed signal at block boundaries. Quantization errors, ringing artifacts, and high frequency noise can also occur. Further, the intensity of the compressed video data may be shifted. Such intensity shift may also cause visual impairments or artifacts. To help reduce such artifacts in decompressed video, three in-loop filters have been proposed for the emerging HEVC standard: a deblocking filter to reduce blocking artifacts, a sample adaptive offset filter (SAO) to reduce distortion caused by intensity shift and high frequency noise, and an adaptive loop filter (ALF) to minimize the mean squared error (MSE) between reconstructed video and original video